1. Field of the Invention
The present invention relates generally to a reciprocating type refrigerant compressor improved so as to prevent leakage of a compressed refrigerant from the cylinder bores in which compression of the refrigerant is carried out by the reciprocation of pistons. More particularly, the present invention relates to an improved internal sealing unit interposed between an end of a cylinder block and a valve plate assembly of a reciprocating type refrigerant compressor in order to tightly seal the periphery of each of a plurality of cylinder bores in which respective pistons reciprocate to suck a refrigerant from a suction chamber, compress the refrigerant, and discharge the compressed refrigerant into a discharge chamber. The reciprocating type refrigerant compressor according to the present invention is intended to be used as a refrigerant compressor incorporated in a vehicle climate control system.
2. Description of the Related Art
U.S. Pat. No. 4,688,997 to Suzuki et al. discloses one of the typical reciprocating refrigerant compressors adapted for use in a vehicle climate control system. The reciprocating refrigerant compressor includes a cylinder block having formed therein a plurality of parallel cylinder bores arranged around an axis of rotation of a drive shaft rotatably supported by the cylinder block and a housing assembly closing the opposite ends of the cylinder block, a valve plate having bored therein a plurality of suction ports and a plurality of discharge ports arranged to open into the respective cylinder bores, a suction chamber, a discharge chamber and, a crank chamber which are defined in the housing assembly, a suction valve interposed between one end of the cylinder block and the valve plate, a discharge valve interposed between the valve plate and the housing assembly, and a plurality of single-headed pistons reciprocating in the cylinder bores for the compression of a refrigerant sucked from the suction chamber and for the discharge of the compressed refrigerant into the discharge chamber. Namely, in the reciprocating refrigerant compressor, the plurality of pistons reciprocate in the cylinder bores in response to the rotation of a cam plate and the drive shaft within the crank chamber and, accordingly, the refrigerant at low temperature and pressure which has entered from an external refrigerating circuit into the suction chamber is sucked into the respective cylinder bores via the suction ports to be compressed by the pistons in the compression chambers formed in the respective cylinder bores. The compressed refrigerant is discharged as the refrigerant gas at high temperature and pressure by the pistons from the compression chambers into the discharge chamber via the discharge ports. The compressed refrigerant is further delivered from the discharge chamber into the external refrigerating circuit of the climate control system.
When the refrigerant is compressed by the pistons within the compression chambers in the respective cylinder bores, the refrigerant at high pressure should be discharged from the compression chambers into only the discharge chamber while being prevented from leaking into a suction pressure area or an exterior of the compressor via an end face area of the cylinder block surrounding the respective cylinder bores. The leakage of the compressed refrigerant reduces the amount of the compressed refrigerant to be used with the climate control system, and therefore, the compressing performance of the refrigerant compressor decreases. Thus, the end of the cylinder block must be appropriately sealed.
The sealing of the cylinder block end and, particularly, the end face area surrounding the respective cylinder bores of the cylinder block, to prevent the leakage of the compressed refrigerant acquires a great importance to the reciprocating refrigerant compressors used with a supercritical-cycle-refrigerating system in which a closed refrigerant-circulation path thereof includes a high-pressure path through which the refrigerant under a high discharge pressure, more specifically, under an supercritical pressure flows.
In the refrigerant compressor incorporated in the super-critical-cycle refrigerating system, the gas of the refrigerant is compressed to have a pressure high above a critical pressure peculiar to the refrigerant. For example, when a carbon dioxide of which the critical pressure is 7.35 MPa is used as a refrigerant, the compressor compresses the refrigerant to a pressure of approximately 10 MPa.
On the other hand, when a fluorinated hydrocarbon gas is used as the refrigerant, and when the refrigerant compressor is incorporated in a refrigerating system operated under a condition such that a discharge pressure and a suction pressure of the refrigerant gas are always kept below a critical pressure of the refrigerant gas (this type of refrigerating system will be hereinafter referred to as a subcritical-cycle-type refrigerating system), the discharge pressure of the refrigerant discharged from the compression chambers of the compressor is approximately 1 through 3 MPa.
Therefore, it will be understood that the discharge pressure of the compressor incorporated in the supercritical-cycle-type refrigerating system is much higher than that of the compressor incorporated in the subcritical-cycle-type refrigerating system.
Accordingly, the sealing of the end face area of the cylinder block around the respective cylinder bores is very critical to the reciprocating refrigerant compressor which is used with the supercritical-cycle-type refrigerating system, in order to prevent leakage of the compressed refrigerant from the cylinder bores into the suction pressure region in the compressor or the exterior of the compressor, via a boundary between the end face area of the cylinder block around the cylinder bores and the confronting face of the valve plate.